Proposal for Phase-2 Pixel Electronics Geometry and Design Considerations

1. Phase-2 pixel “V0” Proposal of a straw-man geometry Phase-2 Pixel Electronics Meeting

2. First ideas presented in April • G. Sguazzoni in the Tracker Upgrade Session @ KIT • https://indico.cern.ch/event/307600/contribution/12/material/slides/0.pdf • Recall some highlights: • Assume large chips of 21×23 mm2 active, 23×23 mm2 physical • Use 4×1 modules in barrel layers 1-2, 4×2 modules in layers 3-4 • The first layer has 10 modules in φ • Several options considered for the forward • “Flower” geometry and “tile” geometry • The tile geometry reduces overlaps • Pixel sizes considered: • Inner parts: 50×50 μm2 or 25×100 μm2 • Outer part: 100×100 μm2 or 50×200 μm2 Implemented over 4 different surfaces Phase-2 Pixel Electronics Meeting

3. Constructive feedback received • Large pixel chip may create issues for bump-bonding • Bump-bonding of FE-I4 was not straightforward • Even larger area should not be taken as starting point • R&D needed! • The mechanics for the “flower” geometry is a priori not more complicated than the “tile” geometry, if the surfaces are flat • In the tile geometry, services come out at some specific φ locations • Redistribution is most likely needed, but might be difficult • Cannot be taken for granted, requires some engineering studies • A pixel of 25×100 μm2 is significantly more difficult than 50×50 μm2 • For planar silicon, and even more for 3D • The best b-tagging algorithms use tracking in 3d • Better performance and higher robustness wrt high pile-up • The performance to first order depends on the pixel area, not the aspect ratio • A square pixel a priori gives higher robustness wrt high pile-up • Possibility to go beyond 140 <PU> is being discussed more and more… • In the forward the main requirement is pile-up mitigation • Requires good z0 resolution on tracks • Some momentum resolution is certainly also desirable • Maybe a square pixel is a simple good balance? Phase-2 Pixel Electronics Meeting

4. Next steps • Define a “Version 0” with reasonably safe assumptions, that can be defended on some solid basis • In future, compare different options in terms of potential performance, risks, cost… • Implement the “pixel V0” in tkLayout and derive basic properties (ongoing) • Translate geometry to CMSSW for full simulation • In parallel: develop toy model for the electronics, to start building a first guess of the detector material Phase-2 Pixel Electronics Meeting

5. The Pixel V0 • Fall back to smaller chips: 17×19 mm2 active, 19×19 mm2physical • Active width of 17 mm is the next “useful” value, as it corresponds to a 12-faces 1st barrel layer (as opposed to 10-faces, discussed @ KIT) • N.B. 2 mm for the end-of-column is a guess; a square chip is a starting point, not a necessity • Such dimensions are slightly smaller than the ATLAS FE-I4: likely doable (although we are still increasing the bump density) • A larger chip can be reconsidered after some successful R&D on bump-bonding • Take square pixels as starting point • 50×50 μm2in the inner region, 100×100 μm2in the outer region • Good combination of all different requirements • I.e. it may not be the optimum, but it’s certainly not a useless configuration to study • Good ground to compare planar silicon and 3D silicon • Benchmark to evaluate possible improvements with different (more complicated) options Phase-2 Pixel Electronics Meeting

6. The Pixel V0 • Barrel • Still consider 1×4 modules in layers 1-2 and 2×4 modules in layers 3-4 • Layer 1 with 12 faces: mechanics could be very similar to the existing one! • All layers have ×4 multiplicity in φ • Length similar to present BPIX obtained with 7 modules • Avoids the annoying feature of the projective hole at z = 0 1×4 2×4 0 0.2 0.4 0.6 0.8 1.0 1.2 0 100 200 Phase-2 Pixel Electronics Meeting

7. The Pixel V0 • Forward • Start with the better-understood “flower” geometry, with flat surfaces • Simplest option • “Tile” geometry can be reconsidered later and compared • Requires some understanding of the services • More complicated 3-d geometries (e.g. turbine) can be studied and compared • Advantages vs complication, amount of material, surface of silicon, etc… • Take inspiration from the double-disk geometry adopted for the Outer Endcap • But with split on the vertical axis! • Cover radial range 32 mm – 160 mm • Hermeticity achievable in a clash-free geometry with ½-size modules wrt the barrel • Use same 50×50 μm2 and 100×100 μm2pixel size as in the barrel 1×2 2×2 Phase-2 Pixel Electronics Meeting

8. Active surfaces Phase-2 Pixel Electronics Meeting

9. Back disk Front disk Phase-2 Pixel Electronics Meeting

10. Active/physical front disk (2 mm for end-of-column) Phase-2 Pixel Electronics Meeting

11. Active/physical back disk (2 mm for end-of-column) Phase-2 Pixel Electronics Meeting

12. All together Outer Tracker Pixel Total Phase-2 Pixel Electronics Meeting

13. All together Outer Tracker Pixel Total Phase-2 Pixel Electronics Meeting

14. Some performance “numbers” • Pessimistic assumptions on resolutions • 10×10 for 50×50 μm2 pixel size, 25×25 for 100×100 μm2pixel size • We should be able to do better than that! • The amount of material is not under control • We do not have a sufficiently detailed concept, yet • Still, what we have in tkLayout is certainly pessimistic, at least in some regions • Let’s look at some numbers nonetheless: • Gives a first hint that what we are doing makes some sense! Phase-2 Pixel Electronics Meeting

15. Thank you! Feedback, as usual, most welcome… Phase-2 Pixel Electronics Meeting